Download 16-17 membrane notes

structure and function
Membrane is a collage of proteins & other molecules
embedded in the fluid matrix of the lipid bilayer
Glycoprotein
Extracellular fluid
Glycolipid
Phospholipids
Cholesterol
Peripheral
protein
Transmembrane
proteins
Cytoplasm
Filaments of
cytoskeleton
1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model
Membrane structure and function
PLASMA MEMBRANE- surrounds ALL cells
• Made of PROTEIN and PHOSPHOLIPIDS
• PHOSPHOLIPIDS = AMPHIPATHIC
= Have both philic and phobic regions
• Form a BILAYER with polar heads out/phobic tails
in
FLUID MOSAIC MODEL
• Current model for animal plasma membrane
• Held together by weak phobic interactions
that make membrane fluid
• Components can move laterally
FLUIDITY of MEMBRANES
• Different species have different FATTY ACID tails in their
phospholipids
• UNSATURATED FATTY ACIDS make “kinks” so
phospholipids can’t pack as close together
(remain fluid @ colder temps)
CHOLESTEROL (in animal cells only)
makes membranes less fluid at higher temps (keep
phospholipids from moving around)
makes membranes more fluid at lower temps (keep
phospholipids from packing closely together)
Membrane Proteins
• Proteins determine membrane’s specific functions
• cell membrane & organelle membranes each have unique
collections of proteins
• Classes of membrane proteins:
• peripheral proteins
• loosely bound to surface of membrane
• ex: cell surface identity marker (antigens)
• integral proteins
• Embedded in lipid bilayer, usually across whole membrane
• transmembrane protein – span entire membrane
• ex: transport proteins
• channels, permeases (pumps)
Proteins domains anchor molecule
• Within membrane
• nonpolar amino acids
Polar areas
of protein
• hydrophobic
• anchors protein
into membrane
• On outer surfaces of
membrane in fluid
• polar amino acids
• hydrophilic
• extend into extracellular fluid &
into cytosol
Nonpolar areas of protein
Many Functions of Membrane Proteins
“Channel”
Outside
Plasma
membrane
Inside
Transporter
Enzyme
activity
Cell surface
receptor
Cell surface
identity marker
Cell adhesion
Attachment to the
cytoskeleton
“Antigen”
OTHER MEMBRANE COMPONENTS
• CARBOHYDRATES (Ex: attached to GLYCOPROTEINS)
~ important in cell-cell recognition/immune system
function and tissue development/ differentiation
EX; important in blood transfusions/organ transplants/recognition
of invaders
by immune system
FUNCTION OF PHOSPHOLIPIDS
• phospholipid tails provide phobic barrier
• separate cell from liquid environment
• SELECTIVELY PERMEABLE- due to hydrophobic/hydrophilic
arrangement of phospholipids
~ allows certain molecules to pass through- non-polar, hydrophobic,
gases (hydrocarbons, CO2 & O2)
~ prevents other substances from passing through- ions,
polar/hydrophilic, large
TRANSPORT PROTEINS/VESICLES assist movement of substances
across bilayer that can’t go on their own